We select a total number of 500 high visual quality images from the DIV2K [1]}, [2]} dataset. For each image, we apply the KLT-based image transform and inverse KLT-based image reconstruction with the first \(k\)  spectral components, \(k=1,2,\cdots ,K\) . Thus, we can obtain \(K\)  reconstructed images for each original image. Then, we conduct a user study to subjectively determine the critical point \(L\in \lbrace 1,2,\cdots ,K\rbrace \)  for each original image. Details of the user study are illustrated as follows.
